Studies on the Changes of Blood Pressure and Heart Rate by Intracerebroventricular Bicuculline in Rabbits

ABSTRACT

To elucidate the role of CNS GABA ergic system in the regulation of cardiovascular function, the effects of intracerebroventricular(icv) bicuculline(BIC), a selective GABAA antagonist, on blood pressure and heart rate were investigated in urethane anesthetized rabbits. 1) Icv BIC produced dose-dependent pressor and bradycardiac effect, while intravenous(iv) BIC had no effect on blood pressure and heart rate. 2) The pressor effect of BIC(10(g) was significantly attenuated by pretreatments with icv ketamine(5 mg) or icv diazepam(0.1 mg, 1 mg). Bilateral vagotomy and pretreatment with icv mecamylamine(0.2 mg), iv chlorisondamine(1 mg/kg), in phentolamine(1 mg/kg) did not affect the pressor action. 3) The bradycardiac effect of BIC(10(g) was abolished or reversed to slight tachycardia by bilateral vagotomy and pretreatment with icv ketamine(2.5 mg, 5 mg), icv diazepam(0.1 mg, 1 mg) and iv chlorisondamine(1 mg/kg). Neither icv mecamylamine(0.2 mg) nor iv phentolamine(1 mg/kg) affected the bradycardia. These results suggest that blockade of GABAA receptor produce pressor action which is associated with central excitatory amino acid system and produce reflex bradycardia induced by the pressor effect, and that sympathetic nervous system might not be involved in the pressor effect.